Synthesis and characterization of thiophene and fluorene based donor-acceptor conjugated polymer containing 1,3,4-oxadiazole units for light-emitting diodes

Article abstract of DOI:10.1016/j.tetlet.2011.10.157

A new donor-acceptor (D-A) conjugated polymer (PDTOF) containing 3,4-didodecyloxythiophene, fluorene and 1,3,4-oxadiazole units is synthesized by using Wittig reaction methodology. The synthesized polymer is characterized by ¹H NMR, FTIR, GPC,

Full text of DOI:10.1016/j.tetlet.2011.10.157

Tetrahedron Letters 53 (2012) 157–161
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Tetrahedron Letters
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Synthesis and characterization of thiophene and fluorene based donor–acceptor
conjugated polymer containing 1,3,4-oxadiazole units for light-emitting diodes
M.G. Murali a, P. Naveen a, D. Udayakumar a, , Vandana Yadav b, Ritu Srivastava b
⇑
a Department of Chemistry, National Institute of Technology Karnataka, Surathkal, PO Srinivasnagar 575 025, India
b Organic Light-emitting Diode Lab, Polymeric and Soft Material Division, National Physical Laboratory, New Delhi 110012, India
a r t i c l e i n f o
a b s t r a c t
Article history:
A new donor–acceptor (D–A) conjugated polymer (PDTOF) containing 3,4-didodecyloxythiophene, fluo-
rene and 1,3,4-oxadiazole units is synthesized by using Wittig reaction methodology. The synthesized
polymer is characterized by 1H NMR, FTIR, GPC, and elemental analysis. The optical energy band gap
of the polymer is found to be 2.42 eV as calculated from the onset absorption edge. The electrochemical
studies of PDTOF reveal that, the HOMO and LUMO energy levels of the polymer are ꢀ5.45 eV and
ꢀ3.58 eV, respectively. The polymer is thermally stable up to 320 °C. Polymer light-emitting diode
devices are fabricated with a configuration of ITO/PEDOT: PSS/PDTOF/Al using PDTOF as the emissive
layer. The electroluminescence (EL) spectrum of the device showed green emission with CIE coordinate
values (0.34, 0.47). By current density–voltage characteristics, threshold voltage of the PLED device is
found to be 6.5 V.
Received 13 September 2011
Revised 28 October 2011
Accepted 30 October 2011
Available online 6 November 2011
Keywords:
Donor–acceptor conjugated polymer
Cyclic voltammetry
PLEDs
Electroluminescence
Ó 2011 Elsevier Ltd. All rights reserved.
In the last two decades, the design and synthesis of electrolumi-
nescent conjugated polymers as the active materials in the field of
polymer light-emitting diodes (PLEDs) have received much atten-
tion because these materials are potential candidates in flat panel
display and lighting applications.1,2 Extensive research has also
been performed to develop highly efficient light-emitting polymers
with tunable emission, long lifetimes, and color purity.3 However
the focus on the area of conjugated polymers has drawn great
interest mainly because of easy processing, low operating voltages,
faster response times, and facile color tuning over the full visible
range, which makes them suitable for large-area flat panel dis-
plays.4 Due to this reason, the design and synthesis of new conju-
gated polymers of varied optoelectronic properties play a vital role
in the area of display technology.5 In this regard, a wide range of
conjugated polymers such as poly(p-phenylenevinylene) (PPV),6
poly(thiophene) (PT),7 poly(pyrrole),8–10 poly(p-phenylene)
(PPP),11 poly(fluorene) (PF),12 and their derivatives have been
extensively investigated as emissive materials in LEDs. It is known
that to obtain highly efficient light emitting devices, the balance in
the injection and transportation of both holes and electrons into
the polymer emissive layer is necessary. Several approaches have
been used in order to achieve high electroluminescence efficiency
in PLEDs.13–15 Among them, donor–acceptor (DA) type polymers,
introduced by Havinga et al.16 in the macromolecular systems via
alternating electron rich and electron deficient substituents along
a polymer backbone are the well known approach to obtain effi-
cient devices.17 In this system, the electron or hole affinity can
be enhanced simultaneously or controlled independently.18,19 In
the categories of conjugated polymers, polythiophene, and polyflu-
orene and their derivatives occupy a significant position. In partic-
ular, polythiophenes are more attractive candidates for PLEDs
because of their good thermal stability both in the neutral and
doped states and their wide electronic and optical tenability.20–22
Also polyfluorene derivatives are attractive active materials for
light-emitting diodes because of their thermal and chemical stabil-
ity and their exceptionally high solution and solid-state fluores-
cence quantum yields.12,23 Moreover, the facile substitution at
the 9-position of the fluorene monomer allows the control of poly-
mer properties such as solubility, processability, and morphology.
Since 3,4-dialkoxythiophene and fluorene derivatives are both
electron rich and hole transporting, it is necessary to introduce
electron withdrawing units to the main chains or side chains to at-
tain large electron affinities. The strong electron withdrawing
1,3,4-oxadiazole unit is the widely used electron injection and hole
blocking material because of its high electron affinity, good ther-
mal, and chemical stability.24,25
Herein we report the synthesis, characterization, and electrolu-
minescent properties of
a new donor–acceptor (D–A) type
conjugated polymer PDTOF. The polymer structure consists of
3,4-didodecyloxythiophene and fluorene moieties as electron
donor units and 1,3,4-oxadiazole moiety as the electron acceptor
unit along with vinylene linkages. The thermal, optical, and elec-
trochemical properties of the polymer are studied. Polymer light-
emitting diodes are fabricated using PDTOF as emissive material
⇑
Corresponding author. Fax: +91 824 2474033.
E-mail address: udayaravi80@gmail.com (D. Udayakumar).
0040-4039/$ - see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2011.10.157

158
M. G. Murali et al. / Tetrahedron Letters 53 (2012) 157–161
with a configuration of ITO/PEDOT: PSS/PDTOF/Al. The EL proper-
ties of PDTOF reveal that the polymer is a green light-emitting
material for efficient light-emitting diodes.
1677 cmꢀ1 due to >NH and >C@O groups, respectively. Cyclization
of compound (2) to bisoxadiazole (3) was achieved by using POCl3
and the completion of the reaction was confirmed by using 1H
NMR and FTIR spectral studies. In the 1H NMR spectrum, the disap-
pearance of two singlet peaks due to >NH protons confirms the
cyclization. Further, the FTIR spectrum of (3) showed no absorption
peaks corresponding to >NH and >C@O groups while a new peak
appeared at 1568 cmꢀ1 due to –C@N– stretching, indicating the
formation of the oxadiazole ring. The synthesis of monomer M1
from compound (3) requires two additional steps (Scheme 1).
The first step consists of bromination of compound (3). The
reaction of Br2 in chloroform with (3) did not give the required bro-
minated product (4). We have tried the method of N-bromosuccin-
imide (NBS) using different solvents like DMF, CCl4, and benzene
which were also unsuccessful. The failure of these methods could
be due to the deactivation of thiophene rings in 3 toward bromin-
ation by the presence of electron deficient 1,3,4-oxadiazole units
attached to the thiophene rings. However bromination reaction
was successful when compound 3 is treated with NBS in trifluoro-
acetic acid/chloroform (3:1) solvent mixture, yielding the dibromo
compound 4 in reasonable yield. The structure of compound 4 was
confirmed by 1H NMR spectrum, which showed the disappearance
of double doublet peak of thiophene ring proton at position 2 and
conversion of all double doublets into doublet peaks. The monomer
M1 was obtained by coupling between dibromo compound 4 and
4-formylphenylboronic acid through Suzuki coupling reaction. 1H
NMR spectrum of M1 showed two (–CHO) protons as singlet at d
The synthetic route for preparing the monomers and the poly-
mer (PDTOF) are outlined in Scheme 126. The detailed synthetic
procedures of the intermediate compounds and their spectral data
are given in the Supplementary data. The final conjugated polymer
(PDTOF) containing 3,4-didodecyloxythiophene, fluorene, and
1,3,4-oxadiazole units is synthesized by using Wittig reaction
method. The chemical structures of all the intermediates and the
polymer were confirmed by NMR spectroscopy, FTIR spectroscopy,
and elemental analysis. The compound 3,4-didodecyloxythioph-
ene-2,5-carbonyldihydrazide (1) was prepared according to the
previously reported method.27 To prepare 3,4-bis(dodecyloxy)-
N’2,N’5-di(thiophene-2-carbonyl)thiophene-2,5-dicarbohydrazide
(2), the dihydrazide (1) was condensed with thiophene-2-carbonyl
chloride in N-methylpyrrolidinone (NMP) in the presence of pyri-
dine at room temperature. Conversion of dihydrazide to dicarbo-
hydrazide was confirmed by 1H NMR and FTIR studies. The 1H
NMR spectrum of 2 showed two >NH protons as singlet at d 10
and 9.39. The three doublet peaks in the range of 7.69–7.68,
7.54–7.52, and 7.10–7.08 ppm are assigned to thiophene ring pro-
tons at positions 2, 4 and 3 respectively. The triplet peak at
4.29 ppm is due to the –OCH2– protons of the alkoxy chains of
the thiophene ring and the multiple peaks in the range 1.96–
0.87 ppm are due to the —(CH2)10–CH3 protons of the alkoxy
chains. The FTIR spectrum of 2 showed sharp peaks at 3380 and
H25C12
O
O
H25C12
N
O
OC12H25
O
OC12H25
N
N
H25C12
O
OC12H25
ClOC
POCl3
S
S
N
S
O
NH
NH
NH
O
NH
3
Reflux 5h
S
H2NHNOC
CONHNH2
NMP/Pyridine
R.T
S
S
S
O
O
2
1
S
TFA / CHCl 3
NBS
RT
B(OH)2
OC12H25
H25C12
O
O
N
H25C12
N
O
N
OC12H25
N
S
S
CHO
O
N
N
OHC
N
S
S
N
Pd (PPh3)4
M1
O
O
Toluene / Ethanol
CHO
4
S
S
aq. Na2CO3
90 oC, 12h
Br
Br
HCHO
C6H13Br
Br
Br-Ph3P+
Br
P+Ph3 Br-
PPh3
DMF
NaH/ DMF
30% HBr
H13C6
H13C6
C6H13
C6H13
H13C6
C6H13
5
6
M2
H25C12
O
O
OC12H25
O
EtOH/CHCl 3
M1
M2
+
C2H5ONa
R.T
S
S
S
N
N
N
N
C6H13
H13C6
PDTOF
n
Scheme 1. Synthetic route of monomers and the polymer.

M. G. Murali et al. / Tetrahedron Letters 53 (2012) 157–161
159
10.05 ppm. The FTIR spectrum exhibited sharp peak at 1690 cmꢀ1
due to >C@O groups. Alkylation of the fluorene was carried out
with DMF, NaH, and n-hexyl bromide to afford compound 5. The
compound 6 and monomer M2 were prepared according to the lit-
erature procedure.28 Finally, the polymerization by Wittig reaction
was confirmed by 1H NMR, GPC, and elemental analysis. The 1H
NMR spectrum of the polymer displayed complex multiple peaks
in the range d 7.97–6.54 ppm corresponding to the aromatic and
vinylic protons. A triplet peak at d 4.32 ppm is due to –OCH2– pro-
tons of the alkoxy chains of the thiophene ring. The multiple peaks
in the range 1.91–0.86 ppm are due to the protons of alkoxy and
alkyl chains attached to thiophene and fluorene rings. The average
molecular weight of the polymer was measured by gel permeation
chromatography (GPC) with reference to polystyrene standards.
The number averaged molecular weight (Mn) of the polymer is
found to be 12200 with molecular weight distribution (PD) 7.
The observed high polydispersity of the polymer may be due to
the aggregation of polymer chains.29 The overall yields for all the
intermediates and polymer were between 55–90%. All the interme-
diate compounds and the polymer showed good solubility in com-
mon organic solvents, such as CHCl3, THF, and chlorobenzene.
The optical properties of the polymer were studied by using
UV–vis absorption and fluorescence emission spectroscopies. The
UV–vis absorption spectra of monomer (M1) solution, PDTOF in
chloroform solution (Ca. 10ꢀ4 g/l) and in thin film state are as
shown in Figure 1. The monomer (M1) solution showed an absorp-
tion maximum at 390 nm. The absorption maximum of the poly-
Figure 2. Fluorescence emission spectra of the monomer (M1) solution, polymer in
chloroform solution and the polymer thin film.
and 40%, respectively, which were calculated by comparing with
the standard of quinine sulfate (ca. 1 ꢁ 10ꢀ5 M solution in 0.1 M
H2SO4 having a fluorescence quantum yield of 55%).34 The optical
properties of the polymer PDTOF is summarized in Table 1.
Cyclic voltammetry (CV) was employed to investigate the redox
behavior of conjugated polymers and to estimate their highest
occupied molecular orbital (HOMO) and lowest unoccupied molec-
ular orbital (LUMO) energy levels, because the onset oxidation and
reduction potentials obtained from the cyclic voltammograms cor-
respond to the HOMO and LUMO energy levels, respectively.35 Fig-
ure 3 shows the cyclic voltammogram of polymer (PDTOF) and
monomer (M1) thin films coated on glassy carbon (GC) disk elec-
trode with 0.1 M tetrabutylammoniumperchlorate (TBAPC)/CH3CN
as the electrolyte at a scan rate of 50 mV/s at room temperature. A
platinum wire and Ag/AgCl were used as counter electrode and ref-
erence electrode, respectively. All measurements were calibrated
with the ferrocene/ferrocenium (Fc/Fc+) standard (EFOC = 0.53 V vs
Ag/AgCl).36 As shown by the cyclic voltammogram, the monomer
(M1) as well as the polymer showed both n-doping and p-doping
processes. The monomer (M1) displayed an oxidation peak at
1.64 V and a small reduction peak at ꢀ1.44 V. These redox proper-
ties of the monomer (M1) could be attributed to the completely
conjugated structure of the molecule and also to the presence of
alternating donor and acceptor groups in the molecule. On sweep-
ing the polymer cathodically, the onset of the n-doping process oc-
curs at the potential of ꢀ0.69 V with a reduction peak at ꢀ1.00 V.
In the anodic scan, the p-doping onset is observed at 1.18 V with
an oxidation peak at 1.44 V. The onset potentials of n-doping and
p-doping processes were used to estimate the HOMO and LUMO
energy levels of the conjugated polymer according to the
equations;37
mer solution at 427 nm corresponds to the
polymer backbone. The polymer film displayed an absorption peak
p–
p⁄ transition in the
at 443 nm. Obviously, the red shift of about 16 nm in the film state
is due to the p–
p⁄ stacking effect. The optical band gap, defined by
the onset absorption of the polymer in the film state is 2.42 eV. The
polymer showed low band gap when compared to those of PFO,
PFV, and some fluorene based conjugated polymers containing
oxadiazole pendants.30–32 This may be due to the strong interac-
tion between electron donor segments (thiophene and fluorene)
and strong electron acceptor segment (1,3,4-oxadiazole) in the
polymer backbone. PDTOF emits green light under the irradiation
of UV light. The polymer in solution showed emission maximum
at 506 nm while in the film state a bathchromic shift of 7 nm is
observed (Fig. 2). This can be attributed to the interchain or/ and
intrachain mobility of the excitons and excimers generated in the
polymer solid state.33 The fluorescence quantum yields of the
monomer (M1) and the polymer in chloroform solution are 23%
ox
ðonsetÞ
red
ðonsetÞ
EHOMO ¼ ꢀ½E
¼ ꢀ½E
þ 4:8 eV ꢀ EFOCꢂ and ELUMO
þ 4:8 eV ꢀ EFOCꢂ; respectively:
ox
ðonsetÞ
red
ðonsetÞ
Where E
and E
are the onset potentials for the oxida-
tion and reduction processes of the polymer, respectively. Accord-
ingly, the HOMO and LUMO energy levels of the polymer are
estimated to be ꢀ5.45 eV and ꢀ3.58 eV, respectively, and hence
the electrochemical band gap is 1.87 eV. The difference between
the electrochemical and optical band gaps can be attributed to
the creation of free ions in the electrochemical experiment com-
pared with the one measured through UV experiment, which refers
to a neutral state.38,39 The electron affinity of the polymer is lower
than those of poly (fluorenevinylenes) (ꢀ2.6 eV), CN-PPV
Figure 1. UV–vis absorption spectra of the monomer (M1) solution, polymer in
chloroform solution and the polymer thin film.

160
M. G. Murali et al. / Tetrahedron Letters 53 (2012) 157–161
Table 1
Optical and electrochemical properties of the polymer (PDTOF)
Absorption and fluorescence emission spectra
Cyclic voltammetry (vs Ag/Ag+)
a
b
a
b
c
d
ox
Eogpt (eV)
fl
EEgC ðeVÞ
red
kmax (nm)
kmax (nm)
kem (nm)
kem (nm)
/
(%)
/
(%)
fl
EHOMO (eV)
ꢀ5.45
ELUMO (eV)
ꢀ3.58
E
(V)
E
(V)
ðonsetÞ
ðonsetÞ
427
443
506
513
2.42
23
40
1.18
ꢀ0.69
1.87
Eogpt optical band gap estimated from the onset wavelength of the optical absorption.
EEgc Electrochemical band gap estimated from the difference between EHOMO and ELUMO
.
a
Measured in chloroform solution.
Cast from chloroform solution.
Fluorescence quantum yield of monomer (M1) in solution.
b
c
d
Fluorescence quantum yield of the polymer (PDTOF) in solution.
Figure 4. TGA plot of the polymer with a heating rate of 10 °C minꢀ1
.
Figure 3. Cyclic voltammogram of the polymer film cast on glassy carbon disk in
0.1 M tetrabutylammoniumperchlorate (TBAPC)/CH3CN solution at 50 mV/s. Inset
shows the cyclic voltammogram of the monomer (M1).
(ꢀ3.02 eV) and some poly (aromatic oxadiazole)s (ꢀ2.8 to
ꢀ2.9 eV).40,41 The lower LUMO level of the polymer indicates that
the incorporation of electron withdrawing oxadiazole segment in-
creases the electron affinity of the polymer and thus lowers the
LUMO level of the polymer. From the high electron affinity value
it can be expected that polymer may show an increased electron
injection and transport properties. It should be noted that incorpo-
ration of the electron rich thiophene and fluorene segments in the
polymer backbone raises the HOMO energy level, leading to a low-
er band gap polymer. The HOMO energy level of the polymer is al-
most similar to that of PPV (5.4 eV).42 This means that the polymer
has a good hole injection ability as PPV when it is used in the fab-
rication of PLEDs. The cyclic voltammetry data of PDTOF are sum-
marized in Table 1.
Thermogravimetric analysis (TGA) was used to study the ther-
mal property of the polymer PDTOF and was carried out under
nitrogen atmosphere at a heating rate of 10 °C/min. The analysis
reveals that, the polymer exhibits good thermal stability. The ther-
mogram given in Figure 4 shows that there is no weight loss till
320 °C and there on the polymer starts decomposing.
To investigate the electroluminescent (EL) behavior of the poly-
mer (PDTOF), PLED devices were fabricated with a configuration of
ITO/PEDOT: PSS/PDTOF/Al where PDTOF was used as the emissive
material. The detailed fabrication procedure is described in the
Supplementary data. The typical EL spectrum of the polymer (PD-
TOF) at a driving voltage of 5 V is as shown in Figure 5 (inset). The
EL maximum of polymer is centered at 524 nm. The PLEDs emitted
green light with Commission Internationale De L’Eclairage (CIE)
coordinates (0.34, 0.47) under a driving voltage of 5 V. The EL
Figure 5. Current density–voltage characteristics and Electroluminescence (EL)
spectrum (inset) of the ITO/PEDOT: PSS/ PDTOF/Al device.
spectra of the polymer were red shifted relative to the correspond-
ing solid state PL spectra which probably result from the increased
radiative decay from the longer conjugated segments during EL.43
Moreover, the presence of longer alkoxy and alkyl chains attached
to thiophene and fluorene rings improves the polymer solubility
and film forming capability which leads to a change in the film
morphology. The current density–voltage characteristics of the de-
vice are as shown in Figure 5 and shows that the current density of
the polymer increases exponentially with the increasing forward

M. G. Murali et al. / Tetrahedron Letters 53 (2012) 157–161
20. Roncali, J. Chem. Rev. 1992, 92, 711–738.
161
bias voltage, which is a typical diode characteristic. The polymer
shows threshold voltage of 6.5 V. The lower threshold voltage
can be attributed to the lower energy barrier for electron injection
from the aluminum electrode.
21. Braun, D.; Gustafsson, G.; McBranch, D.; Heeger, A. J. J. Appl. Phys. 1992, 72,
564–568.
22. Chen, F.; Metha, P. G.; Takiff, L.; McCullough, R. D. J. Mater. Chem. 1996, 6,
1763–1766.
23. Yang, Y.; Pei, Q. J. Appl. Phys. 1997, 81, 3294–3298.
24. Bao, Z.; Peng, Z.; Galvin, M. E.; Chandross, E. A. Chem. Mater. 1998, 10, 1201–
1204.
25. Lee, Y. Z.; Chen, X.; Chen, S. A.; Wei, P. K.; Fann, W. S. J. Am. Chem. Soc. 2001,
123, 2296–2307.
26. The monomer M1 was synthesized by Suzuki biaryl coupling reaction method.
In conclusion, we report the synthesis of a new donor–acceptor
(D–A) type conjugated polymer (PTDOF) containing 3,4-didodecyl-
oxythiophene, fluorene and 1,3,4-oxadiazole units via a Wittig
method. The polymer was well characterized by 1H NMR, FTIR,
TGA, UV–vis absorption, fluorescence emission, and cyclic voltam-
metry techniques. The polymer (PDTOF) showed good solubility
in the common organic solvents such as chloroform, tetrahydrofu-
ran, and chlorobenzene with good film forming properties. The
electrochemical properties revealed that the polymer possesses
high lying HOMO energy levels of ꢀ5.45 eV and low-lying LUMO
energy levels of ꢀ3.58 eV. The thermogravimetric studies indicated
that the polymer is thermally stable upto ꢃ320 °C. The optical band
gap of the polymer is found to be 2.42 eV, which could be attributed
to the D–A structure of the polymer backbone. The polymer light-
emitting diode devices were fabricated with a configuration of
ITO/PEDOT: PSS/PDTOF/Al using the polymer PDTOF as the emit-
ting layer. The emission maximum of the EL spectra originated at
524 nm. The EL spectrum of the polymer was red shifted relative
to its PL spectra. The PLEDs using PDTOF as the emissive layer emit-
ted green light with a CIE coordinate of (0.34, 0.47) under a driving
voltage of 5 V. These preliminary studies of EL properties of the
PLED device show that the polymer PDTOF will be a good candidate
as active material in the field of organic light-emitting diodes.
Under argon atmosphere, to
a mixture of dibromo compound 4 (0.5 g,
0.548 mmol) and 4-formylphenylboronic acid (0.172 g, 1.2 mmol) in toluene
and ethanol 10 ml (1:1 volume ratio), 2 M Na2CO3 (aq) was added. After 30 min
of degassing with argon, 3 mol% (0.119 g, 0.164 mmol) of Pd (PPh3)4 was
added. The reaction mixture was stirred at 80 °C for 12 h under argon. After
completion of reaction (progress of the reaction was monitored by TLC), it was
poured into distilled water and extracted with chloroform. The organic layer
was dried with MgSO4 and concentrated. The crude product was purified by
silica gel column using a mixture of hexane and ethyl acetate (10/2) as an
eluent, giving a yellow fluorescent solid. Yield: 70%. mp: 207–208 °C. 1H NMR
(400 MHz, CDCl3, d): 10.05 (s, 2H), 7.97–7.52 (m, 12H), 4.33 (t, J = 6.8 Hz, 4H),
p
1.92–1.24 (m, 40H), 0.86 (t, J = 6.4 Hz, 6H). FTIR (cmꢀ1): 2917 and 2849 (–C–
H), 1690 (–C@O), 1570(C@N), 1513, 1457, 1379,1288, 1210 1020. Element.
Anal. Calcd for C54H64N4O6S3: C, 67.47; H, 6.72; N, 5.83; S, 9.99. Found: C,
67.35; H, 6.64; N, 5.92; S, 10.10. Synthesis of monomer M2: A mixture of 6 (1 g,
2.02 mmol) and triphenylphosphine(1.32 g, 5.06 mmol) in DMF (10 ml) was
heated for 12 h at 105–110 °C under nitrogen. The reaction mixture was cooled
to room temperature and added was slowly into 100 ml of diethyl ether while
stirring. The white solid was filtered, washed with ether, and dried in a vacuum
oven at 40 °C. Yield: 90%. mp:>200 °C. 1H NMR (400 MHz, CDCl3, d): 8.02–7.82
(m, 30H), 7.58–7.17 (m, 6H), 5.6–5.56 (d, 4H), 1.54–1.50 (m, 4H), 1.16–0.78 (m,
p
16H), 0.2 (br, 6H). FTIR
(cmꢀ1): 3407, 3340, 2921, 2852, 1434, 1109, 744.
Element. Anal. Calcd for C63H66 Br2P2: C 72.40, H 6.37. Found: C 72.32, H 6.42.
Synthesis of polymer PDTOF: A solution of sodium(20 mg, 0.936 mmol) in 2 ml
of anhydrous ethanol was added drop wise at ambient temperature under
argon to a mixture of dialdehyde M1 (0.3 g, 0.312 mmol) and phosphonium
salt M2 (0.35 g, 0.312 mmol) in 6 ml of dry chloroform. The mixture was
stirred at room temperature for 12 h. The reaction mixture was slowly poured
into 100 ml of methanol. The precipitated polymer was filtered off. The crude
polymer was redissolved in chloroform and precipitated in methanol several
times. The product was filtered vacuum dried to obtain the yellow powder.
Yield: 65%. 1H NMR (400 MHz, CDCl3, d): 7.97–6.54 (m, 22H), 4.32 (t, 4H), 1.91–
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.tetlet.2011.10.157.
p
0.86 (m, 66H), 0.76 (t, 6H). FTIR (cmꢀ1): 2917 and 2848 (–C–H), 1573, 1482,
References and notes
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7.68; N, 4.35; S, 7.45. Found: C, 75.32; H, 7.54; N, 4.22; S, 7.52.
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